• Transactions of Materials Processing
• /
• v.24 no.6
• /
• pp.405-410
• /
• 2015

Sheet-forming of Mg alloys is conducted at elevated temperatures (250℃) due to the low formability at room temperature. The high-temperature process often gives rise to surface damage on the alloy (i.e. galling.) In the current study, the frictional characteristics of DLC coating slid against an AZ31 Mg alloy at various temperatures were investigated. The coating has been used widely for low-friction processes. Dry-sliding friction and galling characteristics of an AZ31 Mg alloy (disk), which slid against uncoated and a DLC-coated STD-61 steel (pin), were investigated using a reciprocating-sliding tribometer at room temperature and 250℃. To represent the real sliding phenomena during a sheet metal forming process, single-stroke tests were used (10mm stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, and exhibited a low friction coefficient. However, during sliding at 250℃, severe adhesion occurred between the two surfaces, which resulted in a high friction coefficient and galling.

• Journal of Radiation Protection and Research
• /
• v.37 no.2
• /
• pp.70-74
• /
• 2012

Silicon carbide (SiC) is a promising material for neutron detection at harsh environments because of its capability to withstand strong radiation fields and high temperatures. Two PIN-type SiC semiconductor neutron detectors, which can be used for nuclear power plant (NPP) applications, such as in-core reactor neutron flux monitoring and measurement, were designed and fabricated. As a preliminary test, MCNPX simulations were performed to estimate reaction probabilities with respect to neutron energies. In the experiment, I-V curves were measured to confirm the diode characteristic of the detectors, and pulse height spectra were measured for neutron responses by using a $^{252}Cf$ neutron source at KRISS (Korea Research Institute of Standards and Science), and a Tandem accelerator at KIGAM (Korea Institute of Geoscience and Mineral Resources). The neutron counts of the detector were linearly increased as the incident neutron flux got larger.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.40.1-40.1
• /
• 2013

The HI ring serendipitously found in the Leo I galaxy group is unique in size in the Local Universe. It is ~200kpc in diameter with MHI~$1.67{\times}109M{\odot}$, surrounding a pair of early type galaxies M105 and NGC 3384. Its origin is still under debate whether it is the remnant of formation of a galaxy group (primordial) or formed from stripped material during galaxy-galaxy interaction (tidal origin). Intriguingly a number of dwarf galaxies have been identified along the gas ring (with or without optical counterpart). Various properties of these dwarf galaxies such as dark matter content, color, and/or metallicity will allow us to pin down the origin of this large scale HI ring. We have obtained a mosaicked CFHT MegaCam image and the EVLA HI cube of the large scale gas ring. In this work we present optical and gas properties of dwarf galaxies identified in the CFHT data.

• Structural Engineering and Mechanics
• /
• v.54 no.6
• /
• pp.1153-1174
• /
• 2015

Deployable structures have gained more and more applications in space and civil structures, while it takes a large amount of computational resources to analyze this kind of multibody systems using common analysis methods. This paper presents a new approach for dynamic analysis of multibody systems consisting of both rigid bars and arbitrarily shaped rigid bodies. The bars and rigid bodies are connected through their nodes by ideal pin joints, which are usually fundamental components of deployable structures. Utilizing the Moore-Penrose generalized inverse matrix, equations of motion and constraint equations of the bars and rigid bodies are formulated with nodal Cartesian coordinates as unknowns. Based on the constraint equations, the nodal displacements are expressed as linear combination of the independent modes of the rigid body displacements, i.e., the null space orthogonal basis of the constraint matrix. The proposed method has less unknowns and a simple formulation compared with common multibody dynamic methods. An analysis program for the proposed method is developed, and its validity and efficiency are investigated by analyses of several representative numerical examples, where good accuracy and efficiency are demonstrated through comparison with commercial software package ADAMS.

• Proceedings of the KIEE Conference
• /
• 2006.07c
• /
• pp.1422-1423
• /
• 2006

In our study, the PTFE nozzle ablation in the high-voltage self-blast type $SF_6$ gas circuit breaker was investigated. The test circuit breaker has the structure that the pin electrode is moving and the pressure reservoir volume and the dimension is almost same as commercial 145kv 40kA circuit breaker for similar result in real circuit breaker. The variation of current and arcing time was the range of $36kA_{rms}$(symmetry) - $40kA_{rms}$(asymmetry) and 10-16 ms. From the measured data the tendecy of the mass loss of the nozzle to current load and arc energy was estimated. In this process, the distance from the arc to nozzle(PTFE) surface, area which was exposed to arc and stroke contour was considered. These results will be used to enhance the accuracy of the computational fluid dynamics analysis in circuit breaker and estimate the residual life time of a circuit breaker.

• Proceedings of the KIEE Conference
• /
• 2003.07c
• /
• pp.1595-1597
• /
• 2003

This paper presents the deposition of ${\mu}c$-Si:H thin-film and fabrication of a solar cell by VHF-PECVD method. The ${\mu}c$-Si:H thin films and pin-type solar cells are fabricated using multi-chamber cluster tool system. A 7.4% conversion efficiency was achieved from ${\mu}c$-Si:H thin film solar cells with total thickness less than $5{\mu}m$. The physical characteristic was measured by Raman spectroscopy, Solar cell characteristic was measured under AM1.5 illumination.

• Proceedings of the KIEE Conference
• /
• 1993.07b
• /
• pp.971-973
• /
• 1993

Deflection Yoke(the following, DY) is the important electric device of CRT which deflects R, G, B beans influencing magnetic field produced by yoke coils. Recently, DY is designed to the saddle/saddle type of coils, being proposed for high-definite and high-efficient CRT. This paper presents the optimization of pin-sectioned saddle coil's shape for minimizing gap between desired and practical deflections of electron beams by using Genetic Algorithm. Evolution Startegy is utilized in this paper, since evolution strategy is a kind of genetic algorithms finding the optimized values by choicing the better generation with comparing the parents and their children. Here, the children are generated by only mutations from the normal random variables. Evolution strategy has shown better powerful converge rate than the other genetic algorithms becuase of using only the mutation-operator.

• Current Optics and Photonics
• /
• v.4 no.4
• /
• pp.273-276
• /
• 2020

We report on the relationship between output current for quadrant photodetector (QPD) and bias voltage in silicon-based p-i-n (positive-intrinsic-negative) QPD examined using millisecond pulse laser (ms pulse laser) irradiation. The mechanism governing the relationship was further studied experimentally. The output current curves were obtained by carrying out QPD under different bias voltages (0-40 V) irradiated by ms pulse laser. Compared to other photodetectors, the relaxation was created in the output current for QPD which is never present in other photodetectors, such as PIN and avalanche photodetector (APD), and the maximum value of relaxation was from 6.8 to 38.0 ㎂, the amplitude of relaxation increases with bias value. The mechanism behind this relaxation phenomenon can be ascribed to the bias voltage induced Joule heating effect. With bias voltage increasing, the temperature in a QPD device will increase accordingly, which makes carriers in a QPD move more dramatically, and thus leads to the formation of such relaxation.

• Structural Engineering and Mechanics
• /
• v.68 no.5
• /
• pp.591-601
• /
• 2018

Non-moment beam-to-column connections, which are usually referred to as simple or shear connections, are typically designed to carry only gravity loads in the form of vertical shears. Although in the analysis of structures these connections are usually assumed to be pinned, they may provide a small amount of rotational stiffness due to the typical connection details. This paper investigates the effects of this small rotational restraint of simple beam-to-column connections on the behavior and seismic response of steel braced non-moment resisting frames. Two types of commonly used simple connections with bolted angles, i.e., the Double Web angle Connection (DWC) and Unstiffened Seat angle Connection (USC) are considered for this purpose. In addition to the pinned condition - as a simplified representation of these connections - more accurate semi-rigid models are established and then applied to some frame models subjected to nonlinear pushover and nonlinear time history analyses. Although the use of bracing elements generally reduces the sensitivity of the global structural response to the behavior of connections, the obtained results indicate considerable effects on the local responses. Namely, our results show that consideration of the real behavior of connections is essential in designing the column elements where the pin-connection assumption significantly underestimates design of outer columns of upper stories.

• Nuclear Engineering and Technology
• /
• v.51 no.5
• /
• pp.1314-1321
• /
• 2019

In case of multiple failure scenario, such as LOCA with ECCS failure, the decay heat continues to raise the reactor core temperature, eventually leading to the core voiding. In such scenario the convective heat transfer becomes poor and the majority of the heat transfer from fuel bundle takes place by radiation mode. During this abnormal working condition, if the channel pressure is less than 1 MPa, the PT sags and come in contact with the CT. This results in high rate of heat transfer from contact location to moderator. The present paper aims to capture the temperature profile over a simulated nuclear channel during such scenario at a steady state temperature of $600^{\circ}C$ (Centre pin) at two different configurations of PT i.e. PT concentric with CT and PT contact with CT. The results showed that the bottom nodes of all the components (Fuel bundle, PT and CT) of the simulated channel was greatly influenced by the PT/CT contact. Moreover, higher temperature were observed at top nodes of the PT and outer pins of the fuel bundle. However, no significant variation in temperatures were obtained in fuel bundle and CT in concentric condition.